The capillary flows and forces, (capillary pressure, plasma colloidal osmotic pressure, capillary filtration) and tissue flows and forces, (interstitial fluid pressure, tissue colloidal osmotic pressure and lymph flows) will be measured in a perfused dog lung. The forces and flows will be measured at several capillary pressures in order to establish the importance of each parameter in opposing the formation of interstitial and intra-alveolar edema. In addition, proposed ultrastructural studies will add ned information as to the fluid "leak" sites during the formation of intra-alveolar edema and allow us to relate pulmonary lymphatic protein concentration to that in the interstitial fluids. Since the formation of intra-alveolar edema is a result of changes in the Starling forces and possible membrane disruption then the measurement of these forces coupled with the ultrastructural change will allow us to formulte a more concise model of the relationship between the pulmonary microcirculation, interstitial space and alveolar walls during both normal and abnormal fluid accumulation in lung tissue.